In a typical internal combustion engine, supply air is drawn from the atmosphere through an intake passageway which includes a fuel injector, such as a carburetor. The fuel injector supplies and intermixes metered quantities of liquid fuel with the supply air, and the resulting mixture is then drawn through an intake manifold to one or more cylinders for combustion. The carburetor, or other type of fuel injector, is designed to atomize the liquid fuel or, in other words, to break up streams of the liquid fuel into very small droplets for dispersal into the supply air. However, it is generally recognized that existing fuel injectors are not totally effective in atomizing liquid fuel and mixing it with the supply air. Incomplete fuel atomization and inadequate dispersal of the fuel drops into the supply air results in incomplete fuel combustion and reduced engine efficiency. Further, and perhaps of even greater contemporary concern, incomplete fuel combustion also results in the release of harmful, unburnt hydrocarbons and other noxious gases into the atmosphere through the engine exhaust.
A number of different devices in the prior art have been positioned in internal combustion engines between the carburetor and the intake manifold to more fully atomize the fuel and to more thoroughly intermix it with the supply air. Many of these prior art devices have been designed to swirl the supply air for enhanced intermixture. For example, in U.S. Pat. No. 4,153,028 to Kumm et al, a cylindrical rotor is used to "chop" the fuel-air mixture for greater atomization and improved dispersal. Another device for creating a swirling vortex in the fuel-air mixture is disclosed in U.S. Pat. No. 2,251,371 to Moyer, wherein supplemental fuel is tangentially added to a rotating vortex of supply air in a converging mixing passageway.
A somewhat different approach is taken in U.S. Pat. No. 2,925,257 to Cohn, wherein increased atomization of the fuel is attempted by directing the fuel-air mixture through a multiplicity of low pressure zones. These low pressure zones are formed by a corresponding multiplicity of venturi shaped apertures. Openings leading to a fuel supply are provided in each of the venturi shaped apertures to permit introduction of additional fuel into each of the low pressure zones.
Several other attempts have been made in the prior art to atomize fuel entrained in an fuel-air mixture with screen-like devices interposed in the intake system between the fuel injector and the intake manifold. For example, in U.S. Pat. No. 3,449,098 to Larson, a screen is positioned in an intake passageway immediately beneath a butterfly throttle valve. The screen has a semi-spherical shape to accommodate pivotal movement of the butterfly valve. In U.S. Pat. No. 4,094,290 to Dismuke, a plurality of screens are positioned between a carburetor and an intake manifold of an internal combustion engine. A plurality of balls are then encaged between the screens to provide a whirling effect in the fuel-air mixture.
A screen-like arrangement formed by a stack of aluminum plates having registered apertures are disclosed in U.S. Pat. no. 3,459,162 to Burwinkle. Burwinkle also provides a serpentine passage which extends transversely through the plates for directing heated air to preheat the fuel-air mixture for improved vaporization. A further screen-like member interposed between a carburetor and an intake manifold for heating the fuel-air mixture are disclosed in U.S. Pat. No. 4,078,532 to Smith. In this last mentioned patent, the screen-like member is in the form of a plate having a plurality of indentations on its leading face. The indentations functions as reservoirs for accumulating and heating unvaporized liquid fuel. The Smith plate is conductively heated by the heat of the intake manifold to complete fuel vaporization of the accumulated liquid.
A still further structure for intermixing an fuel-air mixture is disclosed in U.S. Pat. No. 4,215,663 to Gaylord. The Gaylord device includes a spacer having a passageway aligned with the intake system passageway. The sidewalls of the passageway have a plurality of recesses for trapping vortices of fluid as the fuel-air mixture flows through the intake system.
Despite the numerous attempts to solve the above mentioned problems, fully satisfactory solutions for fuel atomization have not been found in the prior art. Many of the prior attempts have, in fact, been counterproductive. Preheating the fuel-air mixture in the intake passage upstream of the intake manifold, for example, tends to cause premature detonation of the fuel. Many of the other attempts have proved to be ineffective or unreliable in operation.